The effects of obesity and caloric intake on biliary lipid metabolism in man was investigated in a series of 23 obese healthy subjects and a group of 23 non-obese controls matched for age, sex, and race. It was found that bile was significantly more saturated with cholesterol in the obese subjects compared to the non-obese controls. When the obese subjects were subjected to weight reduction, a significant reduction in the cholesterol content of bile was noted but there were no differences in the bile acid or phospholipid output. Through the course of these studies supersaturated bile in the obese could be attributed to a single defect in lipid secretion, namely an excessive output of cholesterol. From these studies it was concluded that obesity was characterized by excessive hepatic secretion of cholesterol which results in supersaturated bile, this defect could be ameliorated by weight reduction. ed in vi